GLAST Large Area Telescope Instrument Flight Software Flight Unit Peer Review 16 September 2004

GLAST Large Area TelescopeGLAST Large Area Telescope

Instrument Flight Software Flight Unit Peer Review16 September 2004

Inter-task Communications

Presenter: Sergio MaldonadoAuthor: Anthony WaiteStanford Linear Accelerator Center

[email protected]

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope

mailto:[email protected]

16 September 2004 Flight Unit Peer Review - Inter-task Communications 2

Inter-task Communications: RequirementsInter-task Communications: Requirements

• FSW General Requirements:

– EPU-SIU Interface (5.2.1.1)• The EPU FSW shall communicate with the SIU via a custom CPU-to-CPU

serial message protocol described in [18] – [23].– SC Command Processing by SIU (5.3.3.1)

• The SIU FSW shall receive and process LAT commands from the SC via the CTDB in the order that they are received.

– Command Execution Notification (5.3.3.2)• All LAT commands from the SC shall generate time-tagged telemetry

notification of their dispatch for execution in the order they are received.– Command Completion Status (5.3.3.3)

• The FSW shall generate time-tagged telemetry notification about command completion status (success or general cause of failure) at the time such information becomes available.

– Command Dispatch (5.3.3.4)• Commands from the SC shall be placed into the FSW command dispatch

queue immediately upon receipt.– Command Format (5.3.3.5)

• The FSW shall be able to process commands of the format described in the LAT FSW Telecommand and Telemetry Formats document.


Inter-task Communications: Requirements (cont’d)Inter-task Communications: Requirements (cont’d)

• FSW General Requirements (cont’d):

– Command Execution (5.3.3.6 )• The SIU FSW shall be able to reconfigure and direct the operation of the

instrument through a combination of direct execution of commands from the SC, or by preprogrammed operational sequences triggered by commands from the SC.

– Command Execution Sequence (5.3.3.7)• Immediate (single) commands from different sources shall be capable of

interleaving with other immediate (single) commands and with block commands for uploads and dumps.

– Multiple Block Commands (5.3.3.8)• The FSW shall execute block commands for uploads or dumps serially

(i.e., not simultaneously, not interleaved with other commands).– Data Integrity Errors (5.3.3.9.1)

• The SIU FSW shall validate commands prior to execution in case of an error during transmission.

– Parameter Validation (5.3.3.9.2)• The SIU FSW shall validate command parameters prior to execution.


Components of Inter-task CommunicationsComponents of Inter-task Communications

• These requirements are implemented as an integrated system, built from 4 FSW packages:– The ITC package defines the Inter-task Communications standard:

• ITC defines a common communications standard to unify communications between tasks on either the same or different CPUs.

• It also provides the services to build up tasks that are capable of communicating according to the standard.

• ITC is not itself a task, it’s a toolbox.– The CTS package defines the Command and Telemetry/1553 Service:

• It provides the service layer between applications (high level tasks) and the Command and Telemetry Database (CTDB) hardware driver.

• It is constructed using the ITC toolbox, allowing CTS to present an ITC compliant (uniform) interface to the application layer tasks.

• It provides communication:– Spacecraft to CPU– CPU to spacecraft

– The LCS package defines the LCB Service:• It provides the service layer between applications (high level tasks) and the LCB

hardware driver.• It is constructed using the ITC toolbox, allowing LCS to present an ITC compliant

(uniform) interface to the application layer tasks.• It provides communication:

– CPU to CPU– CPU to SSR

– The LCM package defines the LAT Communications Manager:• It controls the reporting/messaging behavior of all tasks on the system and

provides access to global and task level communications statistics


FSW Layer ModelFSW Layer Model

Applications Layer

Inter-task Communications System (ITC)

Service Layer

Driver Layer

Abstract Communication Layer

Command and Telemetry/1553 Service (CTS)

LCB Service(LCS)

1553 Driver (CTDB) LCB Driver (LCBD)

Housekeeping(LHK)

Spacecraft Attitude/Time

Thermal Control(LTC)

File/Object(LFS)

Pro

cess

Bas

ic S

ervi

ces/

VxW

orks

(P

BS

)

Watchdog(LSW)

Instrument Manager

(LIM)

Charge Injection

Calibration (LCI)

Diagnostics Framework

(LDF)

Spacecraft Messages

(LSM)

Instrument Physics

(LPA)


The ITC Toolbox (1)The ITC Toolbox (1)

• ITC achieves uniformity by defining a single message header format applicable to all communications situations:

Fork queue link

Fork queue handler

Queue item free routine

Queue item free routine parameter

LATp protocol Used by EBM

ITCp protocol

Packet length Packet index

Total length

ITC packet payload(CCSDS packet, bag-o-bytes, …)

Standard header for queueing to a forked task

Packet “autodestruct”

ITC Routing Protocol(task/queue delivery)

LCB Hardware Protocol(used between CPUs)

ITC Packetization Protocol(packetization/reassembly

across CPUs)

On

th

e “L

CB

wir

e”

Wit

hin

a C

PU

CC

SD

S



• ITC pre-allocates resources for a maximum of 256 queues per CPU– Queue-space is segmented

• Maximum of 8 (prioritized) queues per task• Maximum of 32 tasks

• ITC understands four protocols– LAT instrument data (payload is the instrument defined format)– Raw (payload is simply “bag-o-bytes”)– Command (payload contains CCSDS telecommand but task dispatch

handled by the “ITC protocol” (ITCp)– APID (payload contains CCSDS telecommand and task dispatch is based on

the APID)• Tasks wishing to participate must initialize via ITC

– Create an ITC task description (ITC_createTask())– Add queues to task description (ITC_addQueue())– Attach protocol handlers to queues (ITC_attachApid())– Start task

(ITC_startTask())• Once started, the process of sending a message is

– Allocate memory (ITC_allocW())– Fill in the message payload (user does this)– Send to destination (ITC_send())

• Destination specified by Node, Task, Queue



• Node, Task and Queue identifiers are pre-assigned by ITC

– Pre-assigned node list

• Note special nodes– Science Data Interface– Spacecraft

• Broadcast provided for master/slave operations

– Pre-assigned task list

• 17 assigned so far– Includes service tasks

Node ID Usage

0 SIU

1 EPU 0

2 EPU 1

3 EPU 2

4 EPU 3

5 Science Data Interface

6 Spacecraft

7 Broadcast

Task ID Usage

0 Anonymous task (unused)

1 LCM

2 LFS master

3 LFS slave

4 LHK master

5 LHK slave

n Etc.



• Node, Task and Queue identifiers are pre-assigned by ITC

– Pre-assigned queue list

• ITC reserves first two queues for itself

• Names are suggestive only: application writers may choose how to use the six user queues

– Pre-assigned protocol list

• “Command” dispatches:– To task by ITCp protocol– Within task by function code

• “APID” dispatches:– To task by APID– Within task by function code

Queue ID Usage

0 Meta (reserved by ITC)

1 Synch (reserved by ITC)

2 Command Extra

3 Command

4 Control Extra

5 Control

6 Bulk Extra

7 Bulk

Task ID Usage

0 LAT instrument format

1 Raw (bag-o-bytes)

2 Command (CCSDS payload)

3 APID (CCSDS payload)


ITC: Scatter/Gather ProblemITC: Scatter/Gather Problem

EPU 1 responds

after a delay

SIU

EPU 1EPU 0

ISSUER

EPU 0 responds

immediately

• When a master task sends a message requiring a response from multiple slaves, how are the responses synchronized?

• ITC provides the “synch” queue to address scatter/gather:

– When a master sends a message, responses to which must be gathered, a special bit in the message packet header is set and master disables all queues except “meta” and “synch”

– Slave tasks reply to the master on the master’s synch queue

– Once all responses have been received on the master (or transaction times out), master re-enables all queues.


The CTS ServiceThe CTS Service

• Input Processing– Receives CCSDS formatted telecommands from the spacecraft.– Verifies CCSDS header.– Copies bare CCSDS telecommand into standard ITC message (with protocol “APID”)– Uses the ITC dispatch mechanism to do the first tier dispatch: to a task based on

CCSDS APID.

• Output Processing– Provides three ITC user input queues:

• Telecommand (used for sending, for example, the repoint request to the spacecraft).

• High priority telemetry (reserved for “alert” telemetry).• Low priority telemetry (“diagnostic” telemetry).

– Messages appearing on queues are:• Checked for CCSDS compliance (general header format, APID in range, overall

length check).• Forwarded to the CTDB driver for transmission to the spacecraft.

First tier dispatch: to task

Second tier dispatch: to routine within task


The LCS ServiceThe LCS Service

• Input Processing– Receives ITC formatted packets from LCB driver.– Reassembles packets as necessary.– Uses the ITC protocol header to dispatch to task.

• Output Processing– Provides all six ITC user input queues:

• Preserves the queue designation across CPUs.– Packetizes a message as necessary.– Forwards the packets to the LCB driver for transmission.– Provides specialized processing to SSR:

• Strips the ITC protocol from the packet.• Introduces the mandated 0xffffffff framing word.


LCM: ArchitectureLCM: Architecture

• LCM is an application-level task that manages the overall state of the communications system and collects global statistics:– LCM responds to telecommands when the ground requires

information about command processing and the inter-task communications system.

– LCM can also change reporting levels and behavior of user tasks

• Success responses• Error reporting behavior


Inter-task Communications:Inter-task Communications:Commands and TelemetryCommands and Telemetry

• Telecommands (implemented in the LCM application task)

– Task management (these functions apply task by task)

• Suppress reporting of successful command execution

• Alter the “messaging level”

• Request detailed communications statistics (by queue/protocol)– NOTE: CCSDS command counters are in critical housekeeping

– Global functions

• Request statistics on ITC resource usage

• Telemetry

– Task by task

• Generate the command success/failure telemetry– Will not acknowledge spacecraft time/attitude commands– Will not acknowledge good “body” packets of file upload

– Global

• Generate responses to the commands outlined above

GLAST Large Area TelescopeGLAST Large Area Telescope

Backup

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope


ITC, CTS, and LCS Package Layout andITC, CTS, and LCS Package Layout andConfiguration ManagementConfiguration Management

• ITC directly uses the following packages/constituents:– CCSDS, CMX, MSG, PBS, VXW

• CTS uses:– CMX, CTDB, ITC, MSG, PBS, VXW

• LCS uses:– LCBD, CMX, ITC, MSG, PBS, VXW

• LCM uses– LCBD, CMX, ITC, MSG, PBS, VXW

• The dependency tree, constituent list, command and telemetry list, and other configuration management information related to these packages are published dynamically on the FSW Web site at

– http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_ITC.shtml– http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_CTS.shtml– http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_LCS.shtml

http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_CCSDS.shtml

http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_CMX.shtml

http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_MSG.shtml

http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_PBS.shtml

http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_VXW.shtml


http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_CTDB.shtml

http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_ITC.shtml










http://www.slac.stanford.edu/exp/glast/flight/web/a_pnp/Pack_CTS.shtml


The Inter-task Communications SystemThe Inter-task Communications System

CTS/CTX LCS

CTDB LCBD

LATp1553 bus

User Task 1

User Task 2

ITC messageque space

Interaction between service (CTS/LCS) level and driver (CTDB/LCBD) level covered in more detail later

Task 3 Task N


ITC: Architecture (cont’d)ITC: Architecture (cont’d)

ITC

List of message queues for all tasks

1553 packets

CPU-to-CPU LATp packets

LAT-to-CPULATp packets

Internal CPUmessages

Q

Q

Q

Q

Q

Q

Messages are routed to queues

TASK

TASK


Command and Telemetry/1553 Service: Command and Telemetry/1553 Service: ArchitectureArchitecture

• The Command and Telemetry Service operates between application-level tasks and the 1553 driver.

– Allows the inter-task communications system (and hence user applications) to be hardware blind.

– Outbound messages pass through the C&T Service, on to the 1553 driver, and over the interface to the Spacecraft

– Inbound messages are caught by the cCTS task before being passed to the appropriate queue on the user task

User Task

Q

Q

Q

Q

Q

CTS/CTX

Q

Q

Q

Q

Q

1553 driver

(CTDB)

Q

Q

Q(cCTS)

1553 bus

Task 2 Task N


LCS: ArchitectureLCS: Architecture

• The LCB Service operates between application-level tasks and the LCB driver.

– Outbound messages pass through the LCB Service, on to the LCB driver, and then on to other CPUs or to registers on the hardware

– The LCB driver places incoming messages directly on user task queues

• LCB message headers contain a flag to indicate which ITC protocol to use

• Different approach than the C&T Service

User Task

Q

Q

Q

Q

Q

LCS

Q

Q

Q

Q

Q

LCB driver

(LCBD)

LATp

Dispatched directly to tasks using 1 of 4 ITC protocols

Task 2 Task N

GLAST Large Area Telescope Instrument Flight Software Flight Unit Peer Review 16 September 2004

Documents

Transcript of GLAST Large Area Telescope Instrument Flight Software Flight Unit Peer Review 16 September 2004